This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Herpes simplex viruses type 1 and 2 (HSV-1 and HSV-2) are highly prevalent human pathogens that cause oral and genital sores, encephalitis, keratitis and fatal infections in newborns. To enter cells, HSV, like any enveloped virus, must fuse its lipid membrane with that of the cell. Entry of HSV into host cells is mediated by four conserved surface glycoproteins, gD, gB, and gH/gL complex. gD binds a specific receptor on the host cell surface and signals to either gB or gH/gL. Both gB and gH/gL complex are indispensable for membrane-fusion. Recently published crystal structure of gB suggested that gB is a viral fusion protein. However, gB alone cannot perform fusion;gH/gL is also essential. No structural information is available on gH/gL, and its exact role in fusion is unknown. Determining the structure of gH/gL will help understand the function of gH/gL and thus the mechanism of the fusion process of herpesviruses. It may also provide important insights for therapeutic intervention.gH/gL is a heterodimeric complex of two viral surface glycoproteins, gH that is anchored on the viral membrane and gL which is bound to gH on the viral surface. I overexpressed, purified, and crystallized the recombinant gH/gL complex in a soluble form. Crystals grow to ~100 m in longest and ~20 ?m in the shortest dimension and diffract to ~3.2 A, albeit anisotropically. I collected several native datasets to 3.5 A from crystals cryopreserved in several different cryoprotectants. The space group is P41(3)212 with a=b=88 A, c=330 A, ?=?=?=90[unreadable]. I will optimize my cryopreservation protocol to improve the resolution and reduce anisotropy.Since no structures of homologous proteins are available for molecular replacement methods, I plan to obtain the phase information by MIR, MAD, or SAD phasing, which I would like to do at the Rapidata 2009 course. Production of Se-Methionine derivative and heavy atom soaks are being done right now. This will be the first description of gH/gL complex structure and will help in explaining the functions of gH/gL.